Fix inertial transformation

[astrojuanlu]

(Asked in the Cesium forum)

When enabling the icrf function on the JavaScript side implemented here:

czml3/src/czml3/widget.py

Lines 26 to 40 in 7b8ba68

	// To have an inertial (ICRF) view
	function icrf(scene, time) {{
	var icrfToFixed = Cesium.Transforms.computeIcrfToFixedMatrix(time);
	if (Cesium.defined(icrfToFixed)) {{
	var camera = viewer.camera;
	var offset = Cesium.Cartesian3.clone(camera.position);
	var transform = Cesium.Matrix4.fromRotationTranslation(icrfToFixed);
	camera.lookAtTransform(transform, offset);
	}}
	}}
	// Temporarily disable inertial view
	// until we make it work with 2D Mercator view
	// and fix the zoom sensitivity, see
	// https://groups.google.com/d/msg/cesium-dev/vuXmepd4T2E/i71tq2I8EAAJ
	// viewer.scene.postUpdate.addEventListener(icrf);

There are some strange effects when rotating the view or switching to 2D. We should try to fix those.

[astrojuanlu]

We already have a potential solution proposed by @OmarShehata:

I think you may need to detect and disable the inertial frame logic when the camera is morphing and/or when it's in 2D view. You can listen to the morph event here:

https://cesium.com/docs/cesiumjs-ref-doc/Scene.html?classFilter=scene#morphStart

And detect whether it's in 2D/3D here:

https://cesium.com/docs/cesiumjs-ref-doc/Scene.html?classFilter=scene#mode